Pipe-type cable comprising aluminum conductors with high-elastic-modulus tensile strands

ABSTRACT

Aluminum pipe-type cable conductors comprise high elasticmodulus core strands so that long continuous lengths can be pulled into a pipe.

i [72] Inventor United States Patent Walter J. Plate Rye, NY.

[21] Appl. No. 22,460

[22] Filed Mar. 25, 1970 [45} Patented Oct. 19, 1971 [73] Assignee Anaconda Wire and Cable Company [54] PIPE-TYPE CABLE COMPRISING ALUMINUM CONDUCTORS WITH HIGH-ELASTlC-MODULUS TENSILE STRANDS 9 Claims, 4 Drawing Figs.

[52] U.S. Cl 174/26 R, 174/1 14 S, 174/130 [51] Int. Cl H011) 9/06 [50] Field of Search 174/10, 24,

25 R, 25 G, 26 R, 266, 103, 108, 113 R, 113 A, 113 C, 114R, 114 S, 116, 119 R, 128, 129 R, 129 5,130,131,131A

[56] References Cited UNITED STATES PATENTS 2,125,869 8/1938 Atkinson 174/114 S UX 2,325,549 7/1943 Ryzowitz 2,432,603 12/1947 Zink 174/129 S X 2,516,747 7/1950 Bennett. 174/25 R 2,538,019 1/1951 Lee 174/113CX 2,665,328 l/1954 Atkinson et a1 174/25 R 2,778,870 1/1957 Nolan; 174/128 3,047,652 7/1962 Ege 174/108 3,080,446 3/1963 Volk... 174/25 R 3,180,925 4/1965 Ege 174/130 X FOREIGN PATENTS 304,031 1/1929 Great Britain 174/128 OTHER REFERENCES Anaconda Bare and Weatherproof Aluminum Wire and Cable, Catalogue No. C78, published by Anaconda Wire and Cable Co., 1949, page 4 relied on. Copy in 174-130.

Ayers, Electrical World, March 24, 1952, page 129. Copy in 17425 R.

Primary ExaminerLaramie E. Askin Attorney-Victor F. Volk ABSTRACT: Aluminum pipe-type cable conductors comprise high elastic-modulus core strands so that long continuous lengths can be pulled into a pipe.

PATENTEUnm 19 l9?l INVIiN'l'OR.

WALTER J. PLATE Ill! 4057/ 1 PIPE-TYPE CABLE COMPRISING ALUMINUM I CONDUCTORS WITH I-IIGI-I-ELASTIC-MODULUS TENSILE STRANDS BACKGROUND OF THE INVENTION High-voltage power cables, of the class known as pipe-type, have paper-tape insulated conductors housed within highpressure pipes that contain insulating oil or gas maintained at high pressure. In the manufacture of such cables the pipes are first-buried in sections, the sections are welded together, and the pipe is tested for pressure tightness. When the pipe has been thoroughly cleaned and dried, the conductors, which have meanwhile been brought to a manhole, are pulled in by a tow line that has been previously threaded through. When the conductors are pulled in they drag along the inside surface of the pipe and, to protect the insulation, each of the conductors is, during its manufacture, overwound with a helically applied, D-sh'aped skid wire. The frequency of manholes and joints is dictated, essentially, by the length of continuous conductor that can be pulled, and this, in turn, depends on either of two factors: the ability of the conductors to withstand the pulling load, and the length of conductor that can be shipped on a reel. Generally considered, copper conductors can withstand pullingloads sufficiently to make reel capacity the determining factor for the length between joints. This however, is not the case for aluminum, with the result that, in spite of its much lower cost; aluminum has not, up to the present, been significantlyadopted for us in pipe-type cables.

A controlling factor for the length of conductor that can be pulled into a pipe is the elongation of the conductor during installation. lndustrypractice limits, the permissible elongation to 0.2 percent. When this limitation is applied to a consideration of the conductormaterial it will be understood that the much higher elastic modulus of copper, compared to aluminum, accounts for its greater ability to withstand pulling loads.

It will be readily understood that large economies will result from a reduction in the number of joints and manholes required of a pipe-type cable and by means of my invention I propose to reduce this number by increasing the length of conductor that can be pulled into a pipe.

I also propose to make practical the use of aluminum for pipe-type cable conductors.

SUMMARY I have invented a pipe-type cable with an insulated conductor that comprises a high elastic modulus tensile strand, preferably steel, and a layer of aluminum forming an electrical conducting core surrounding the tensile strand. The conductor has a wall of taped insulation surrounding the conductor strands, a conducting shielding layer surrounding the insulation and a helical skid wire surrounding the-shielding layer. A plurality of sections of interconnected rigid pipe, which may include at least one angle or comprise a-grade having the effect of increasingthe force required to pull the conductor, contain the conductor and are filled with an insulating fluid under pressure which also penetrates the insulation. For transmitting 3-phase current my cable ill comprise three of the above described conductors within the pipe sections.

I have invented an insulated conductor for a pipe-type cable comprising at least three high-elastic modulus tensile strands, preferably of steel. A plurality of aluminum conductor wires that are compressed into a shaped sector surround each of the strands and are fitted together to form a substantially circular core. A wall of taped insulation surrounds the core, a conducting shielding layer surrounds the insulation, and is in turn surrounded by a helical skid wire. An additional high elasticmodulus tensile strand may be comprised in the center of the COI'C.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a section of a pipe-type cable of my invention. FIG. 2 shows a section of a pipe-type cable conductor made to my invention.

FIG. 3 shows a section'of a "segmentar cable conductor made to my invention.

FIG. 4shows a plan view of a cable installation made in accordance with my invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT In FIG. I a pipe-type cable, indicated generally by the numeral 10, is comprised of a pipe 11 capable of withstanding high pressures such as 200 pounds per square inch of an insulating fluid shown here as an oil but which-may also be a gas such as nitrogen or fluorocarbon within the scope of my invention. The pipe 11 is rigid and is built up of sectional lengths or sections having jointures 13 as shown diagrammatically in FIG. 4. The cable of FIG. I, intended for 3-phase service comprises three insulated conductors I4, 15, 16 which have been pulled into the pipe 1 1 simultaneously. The insulated conductors l4-l6 are each characterized as comprising a plurality of aluminum wires 17, forming the power conducting core surrounding a steel tensile strand 18. As seen in FIG. 2 the strand [8 is comprised of a plurality of steel wires 19, stranded together. In some cases, however, a single steel wire may suffice, depending on the size and desired pulling length of the insulated conductor. The aluminum wires of the cables 14-16 are concentrically applied over the steel in sufficient quantity to supply the desired current carrying capacity. Since the cable 14, and indeed, pipe-type cables generally, are invariably intended for very high voltage service, a conventional strand shielding 21 is applied over the aluminum strands. Over the aluminum core and the stand shielding 2] there are helically wrapped a large plurality of paper tapes 22 building up an insulating layer 23 sufficient for the cable voltage plus a usual factor of safety. Although I have preferred to show paper tapes for the layer23 it is also known to apply other dielectric tapes such as those described in US. Pat. Nos. 3,105,872, 3,077,514 and 3,078,333 and I intend that such other insulating tapes shall be included within the scope of my invention. The oil 12 or other pressurized fluid penetrates the insulation 23, although the presence of other oils, having higher viscosity and applied to the tapes 22 in the taping operation as described in US. Pat. No. 3,378,4 l9 may prevent its immediate diffusion down to the conductor. The penetration of the oil 12 has the effect of raising the pressure of any oil already impregnating the tapes and thus increasing its insulating properties. 7

A layer of insulation shielding 24 is applied over the insulation 23 and bronze skid wires 26 are helically wound around the entire completed insulated conductor. When particularly large conductor areas are required in a cable it is known to employ an industry designated "segmental" conductor stranding which divides the cross section of the conductor into approximate sectots of a circle that are insulated from each other. This has the purpose of reducing "skin effect and hence the AC/DC resistance ratio. A segmental" conductor made to may invention is shown in FIG. 3. Here the conductor, indicated generally by the numeral 27 has an outer structure comprising strand shielding 21, insulation 23, insulation shielding 24 and skid wires 26 not essentially different from the conductor 14, but it also comprises a segmental conductor 28 made up of four sectors 29, 30, 31, 32 each of which has a central steel tensile wire 33. The sectors 29-32 are formed by stranding aluminum wires in a known manner except that the center of each strand is comprised of the steel wire 33. After the round strands have been made they are passed through rolls or shaped dies that distort them into sectors of which there are four in the conductor 27, but fewer or greater numbers of sectors might also be employed within the scope of my invention. I have used the word compressed in this application to refer to the distorting of the steel-cored strands into sector shapes without necessarily crushing the individual wires of the strands. The strands can be further crushed or "compacted to eliminate or greatly reduce the interstices. Such compacting can be done within the scope of my invention and will have the effect of reducing the space required for the conductor, and the amount of oil trapped therein. The sectors 30, 32 are wrapped with thinlayers 34 of insulating tape to insulate them from the sectors 29, 31 along the length of the cable and reduce the skin effect as hereinabove disclosed. The geometry before compressing of the sectors 29-32 dictates to some extent the size of the steel tensile strands 33 and if a greater area of high elastic modulus is required an additional steel strand 36 which may be a single wire or a plurality of wires stranded together may be incorporated in the center of the conductor 27 replacing some filler 37 which with fillers 38-41 are used to solidify and round out the conductor core.

In FIG. 4 a cable installation indicated generally by the numeral 42 is shown extending between two manholes 43, 44 within which lengths of conductor are spliced and which are connected by a large number of sections of the pipe 11 connected at jointures 13. The cable 42 between the manholes is comprised of a straight level length L,, a short straight sloping length L,, and another straight level length L Two 90 bends 46, 47 connect the sloping length L to the lengths L and L Although my invention has great utility for straight level cable installation its advantages are made more manifest in an installation such as that of FIG. 4 comprising slopes and/or bends since these require greater pulling force on the conductors.

TABLE 1 138 KV Aluminum Pipe-type Cables Example A B C D Steel Stranding none 7/0.l36" none 19/0086" Aluminum inches 61/0128 54I0.l36" 6| 54 Size MCM I000 1000 1000 1000 Construction it. 1.. r r Weight, lbl./M' 3150 3600 2950 3530 Max. pull, lbs. 7050 l2l00 7050 12600 Pipe dianL, in. 6 s 6 o Pulling length, it 5600 8 l 50 6200 8850 Shipping length, n. 7500 1200 3500 7500 TABLE 2 138 KV Aluminum Pipe-type Cables Example E F G H Steel stranding none 19/0086" 4-0.1!0" 4-0.110" Aluminum 4-37 4-37 4-36 4-36 Size MCM I500 I500 I500 1500 Construction g g c Weight, |bl./M 4100 4560 4280 4230 Max. pull, lbs. 10600 16100 13200 th l2500 Pipe diam, in. 8 8 8 8 Pulling length, R. 7600 10200 9000 8700 Shipping length, n. 5000 5000 $600 5600 In the tables the constructions of examples A, C, and E are conventional, and examples B, D, F, G, H embody my invention and include steel tensile strands. The designations 7/0.l36 0.136 inches and 19/0086 inches indicate that the steel strands are formed of seven wires, each having a diameter of 0.136 inches, and of 19 wires, each having a diameter of 0.086 inch, respectively. in examples F, G, and H, of segmental" construction F has only one 19/0086 inches steel strand at the center, H and G have one 0.110 inch steel wire in each sector but G has an additional 0.130 inch steel wire at the center. In the compact and segmental construction the tables state the number of wires but not their individual sizes. The notation, 4-37, means four sectors each with 37 aluminum wires. The pulling lengths of the table refer to straight pulls of three conductors, without bends or inclines in the pipe. If we now compare examples C and D we find that the possible distance between joints has been increased by 1300 feet by the addition of center high elastic modulus steel strands in 1,000-

MCM (thousand circular mils) aluminum compact round confeet to 7500 feet by the enlargement in conductor cross section due to the steel, but the 8500-foot capacity was fictitious in the case of example C since the length that could be pulled into the pipe was limited to 6200 feet by the conductors ability to withstand the pulling force. The shipping lengths depicted in the tables represent the capacity of the assignee's largest reel which has a flange diameter of 142 inches.

Since the shipping lengths of cables smaller than 1000 MCM are greater than those of 1000 MCM or larger, it is apparent that the benefit of my invention can be realized for all sizes under 1000 MCM. In other words, my improvement permits advantage to be taken of the large capacity of the shipping reel, which is wasted in examples A and C. For larger conductor sizes the advantages of my invention occurs principally where the pulling length has been limited by bends or inclines in the cable run. A method of calculating the effects of bends and inclines has been fully discussed by R. C. Rifenburg in American Institute of Electrical Engineers Transactions, vol. 72, part Ill, pages 1275-88. in practice, these bends and inclines create a factor that can be deducted from the allowable pulling length of the cable. Thus in FIG. 4 the straight length L is 2500 feet, the bend 46 is the inclined length L: is 300 feet with a 10 incline, the bend 47 is 90 and the length L:, can be established by the length of cable that can be installed. Using standard methods of calculation the effect of the combined slope and bends is to reduce by 3455 feet the allowable pulling length of the conductors. lf, bearing this in mind, we again consider the tables we are required to deduct 3455 feet from each of the tabulated pulling lengths. This results in pulling lengths for examples E, F, G and H of 4145, 6745, 5545, and 5245 respectively. All of these are below the capacity of the reel so that the pulling length rather than the shipping length will be the determining factor for the distance that can be permitted for L This distance L, is seen, then, to

be greater for the conductors of examples F, G, and H made to my invention, than for the conventional conductor of example E.

Although, because of its high elastic modulus ready availability, and relative economy, 1 have preferred to employ steel for my tensile strands 18, 33 and 36, the use of other high modulus strands such as molybdenum, and fiberglass are also included within the scope of my invention.

The foregoing description has been exemplary rather than definitive of my invention for which I desire an award of Letters Patent as defined in the following claims.

lclaim:

1. A pipe-type cable comprising:

A. an insulated conductor comprising:

1 a high-elastic-modulus tensile strand,

2. a layer of aluminum forming an electrical conducting core surrounding said tensile strand,

3. a wall of taped insulation surrounding said conducting core,

4. a conducting shielding layer surrounding said insulation, and

5. a helical skid wire surrounding said shielding layer,

B. a plurality of sections of interconnected rigid pipe containing said insulated conductor, and

C. insulating fluid under superatmospheric pressure filling said pipe sections and penetrating said insulation.

2. The cable of claim 1 wherein said tensile strand comprises steel.

3. The cable of claim 1 wherein said pipes form at least one angle having the effect of increasing the force required to pull in said conductor.

4. The cable of claim 1 wherein said pipe comprises a grade having the effect of increasing the force required to pull in said conductor.

5. The cable of claim 1 comprising three of said insulated conductors within said pipe sections for transmitting 3-phase current.

6. An insulated conductor for a pipe-type cable comprising:

7. The conductor of claim 6 comprising an additional highelastic-modulus tensile strand at the center of said core.

8. The conductor of claim 7 wherein said tensile strands comprise steel.

9. The conductor of claim 6 wherein said tensile strands comprise steel. 

2. a layer of aluminum forming an electrical conducting core surrounding said tensile strand,
 2. The cable of claim 1 wherein said tensile strand comprises steel.
 3. The cable of claim 1 wherein said pipes form at least one angle having the effect of increasing the force required to pull in said conductor.
 3. a wall of taped insulation surrounding said conducting core,
 4. a conducting shielding layer surrounding said insulation, and
 4. The cable of claim 1 wherein said pipe comprises a grade having the effect of increasing the force required to pull in said conductor.
 5. The cable of claim 1 comprising three of said insulated conductors within said pipe sections for transmitting 3-phase current.
 5. a helical skid wire surrounding said shielding layer, B. a plurality of sections of interconnected rigid pipe containing said insulated conductor, and C. insulating fluid under superatmospheric pressure filling said pipe sections and penetrating said insulation.
 6. An insulated conductor for a pipe-type cable comprising: A. at least three high-elastic-modulus tensile strands, B. a plurality of aluminum conductor wires compressed into a shaped sector around each of said strands, said sectors being fitted together to form a substantially circular core, C. a wall of taped insulation surrounding said core, D. a conducting shielding layer surrounding said insulation, and E. a helical skid wire surrounding said shielding layer.
 7. The conductor of claim 6 comprising an additional high-elastic-modulus tensile strand at the center of said core.
 8. The conductor of claim 7 wherein said tensile strands comprise steel.
 9. The conductor of claim 6 wherein said tensile strands comprise steel. 